1. Field of the Invention
This invention relates generally to toilets, and more specifically, to the design of tanks which are used to store a quantity of water used to flush effluent from the toilet bowl.
2. History of the Prior Art
In the Western world, the earliest plumbing systems were developed to dispose of human wastes. Nearly simultaneous development of sewage disposal systems occurred in several locations in the ancient world. The earthenware pipes, masonry sewers, and toilets installed in about 2,500 B.C. in Mesopotamian cities (now included in present day Iraq), are still in working order. In the Indus Valley in what is now Pakistan and western India, most dwellings had drains for waste disposal by about 2500 B.C. A palace built on the island of Crete about 2000 B.C. had primitive toilets and a drainage system with air shafts that served as vents. The Romans contributed to the development of modem plumbing systems by constructing distribution systems for potable water, using lead pipes and fixtures.
After the fall of the Roman Empire in 476 A.D., the quality of plumbing declined throughout the Western world. During the Middle Ages, people disposed of waste materials by throwing them into the street. Although a type of flush toilet was developed in the 1500's, it did not come into wide use because of the general lack of plumbing and sewer systems. During the 17.sup.th century, many cities throughout the world began to construct water and sewer systems. In 1778, Joseph Bramah, an English cabinet maker, patented an improved flush toilet. By 1800, toilets had become common in England. But most of them drained into cesspools, which often overflowed. Septic tanks were invented in the mid-1800's, and a modem sewer system began operating in London in the 1860's.
For nearly two hundred years following the patenting of Joseph Bramah's improved flush toilet, though thousands of U.S. patents were granted for improvements to the device, the functional design of the fixture changed very little. Aesthetic improvements to the device were a major focus of inventors. Some of the efforts aimed at improving the aesthetics of the humble fixture actually degraded its performance rather dramatically. For instance, in the mid-1970's, a low profile toilet was manufactured that had rather abysmal flush performance as a result of the low potential energy of the water stored within the supply tank.
Several decades ago, water conservation suddenly became the rage. The standard tank-type toilet, which used about five gallons of water per flush cycle came under attack. In order to reduce water consumption, it became common to place bricks at the bottom of the supply tank Flush performance was somewhat decreased as a result. Then, in 1992, the U.S. Congress passed a national standard for new toilets, limiting them to 1.6 gallons (approximately 6.76 liters) per flush cycle. In some foreign countries, such as Singapore, where potable water is scarce, new toilets will be limited to only 4.5 liters per flush cycle.
The key to improving flush performance and decreasing water consumption is tank pressure. Europeans have long known that flush performance can be dramatically improved by elevating the toilet's supply tank to ceiling level. However, in the U.S. at least, that design is ignored because installation is more time consuming and the aesthetics of the device are apparently unacceptable. Many new water-efficient toilets available in the U.S. incorporate a supply tank that is pressurized by the water main. Such toilets provide acceptable flush performance using only about 1 and 1/2 gallons, or slightly less than 6 liters, of water. These toilets suffer from three major disadvantages. Firstly, they are considerably more expensive than a conventional toilet with an unpressurized supply tank. Secondly, in areas where water pressure is low or is variable over a wide range, flush performance will be unacceptable at least some of the time. Thirdly, the tank flush valve is more complex and not easily repaired by untrained service personnel.
Unpressurized toilets using 6.76 liters of water per flush are also available in the U.S. The problem with these devices is that flush performance is generally marginal. Consequently, many consumers tamper with the fill and flush mechanisms so that the water released per flush cycle is increased. Often the amount exceeds 13.0 liters per flush cycle. Another remedy for poor flush performance is double or triple flushing of the system. Many replacement components are available for these water-efficient toilets. However, there is no guarantee that a repaired toilet will conform to the original specifications. Another problem with water-efficient unpressurized toilets is the flapper component of the tank flush valve. Chlorine tends to deteriorate the rubber from which they are made, resulting in a device which may leak more water than it uses for operation.
What is needed is a toilet having low cost in combination with high performance flush characteristics, low water consumption, ease of maintenance, and a high degree of tamper resistance.